Technical Field
The present invention relates to an iron-based sintered sliding member and to a production method therefor, in which a powder metallurgical method is used. In particular, the present invention relates to an iron-based sintered sliding member, which exhibits superior wear resistance and sliding characteristics under high surface pressures, and the present invention relates to a production method therefor.
Background Art
For example, in sliding members having sliding surfaces to be applied with high surface pressure, such as driving portions and sliding portions of vehicles, machine tools, or industrial machines, etc., a carbon steel which was cut and was quench hardened and tempered, or a sintered alloy, is used. Specifically, since the sintered alloys can have self-lubricating characteristics by infiltrating lubricating oil thereinto, they can have superior seizure resistance and wear resistance and are thereby widely used. As a sliding member made of such a sintered alloy, for example, a bearing is disclosed in Japanese Patent Application of Laid-open No. 11-117940. The bearing has a sliding surface provided with an iron-based sintered alloy layer consisting of 10 to 30 weight % of Cu and the balance of Fe.
In addition, an iron-based sintered alloy for a sliding member is disclosed in Japanese Patent Application of Laid-open No. 2009-155696. The iron-based sintered alloy consists of, by mass %, 0.6 to 1.2% of C, 3.5 to 9.0% of Cu, 0.6 to 2.2% of Mn, 0.4 to 1.3% of S, and the balance of Fe and inevitable impurities. The iron-based sintered alloy has a structure in which 1.0 to 3.5 mass % of a MnS phase and at least one of a free Cu phase and a free Cu—Fe alloy phase are dispersed in a martensite matrix.
Since the cost of copper metal has been rising in recent years, the technique of using 10 to 30 weight % of Cu as in the case disclosed in Japanese Patent Application of Laid-open No. 11-117940 has relatively high cost in production and is not practical. In addition, Cu has a low melting point and thereby generates a liquid phase in sintering. Therefore, when the amount of Cu is great, dimensional change of a material for a sliding member before and after the sintering is large. In this case, machining is required in order to satisfy a necessary accuracy, which also increases the production cost.
When Cu is added in a sintered alloy, a soft Cu phase or a soft Cu alloy phase is dispersed in a matrix. Therefore, the degree of wear characteristics with respect to a mating member is decreased, and adaptability to the mating member is improved because the sintered alloy is adequately deformable. Conversely, if the amount of Cu is small, the wear resistance is decreased, and the degree of wear characteristics with respect to a mating member is increased. Moreover, in this case, squeal noises occur if the lubricating oil is insufficient.
In view of this, in the invention disclosed in Japanese Patent Application of Laid-open No. 2009-155696, 1.0 to 3.5 mass % of the MnS phase is dispersed. Thus, the decrease of the wear resistance and the increase of the wear characteristics with respect to a mating member due to decrease in the amount of Cu are avoided. However, the MnS phase is generated by adding a MnS powder to a raw powder, whereby it has low fixability with respect to the matrix and may be exfoliated during sliding.